Defective cellular immune function in individuals with the Acquired Immuno-deficiency Sydrome (AIDS) is associated with their development of opportunistic infections and malignancies. The agent(s) responsible for this syndrome and the mechanism accounting for the immune incompetence in these individuals remain unknown. We have characterized a naturally occurring immunosuppressive disease in Macaca cyclopis monkeys. We will use these animals as well as materials from humans with this syndrome to elucidate the nature of the cellular defects in AIDS which lead to the development of cancer. We will furthermore utilize these monkeys in studies to isolate causative agents in AIDS.